Heat treatment of alloy glass machine castings



HEAT TREATMENT OF ALLOY GLASS MACHINE CASTINGS No Drawing. ApplicationJuly 31, 1933, Serial No. 682,954

2 (Claims. (Cl. 148-215) This invention relates to the manufacture of animproved chromium alloy especially adapted for use in the formation ofmetallic appliances employed in glass working machines for mouldingglass into useful articles, and a principal obiect of the inventionresides in the manufacture of metallic parts, used in the glass industryfor pressed were, by employing a novel alloy composition and subjectingit to an improved heat treatment, which are conjointly necessary toincrease the life or usefulness of any machine part subjected to thesevere corrosive and erosive action encountered in the operation of highspeed automatic glass article forming machines.

Although it is to be understood that a large number of different partsused on glass making machinery can be made from the alloy formed as aresult of the present invention, the following description is confinedto plungers for use in the manufacture of pressed glass ware. Heretoforethese plungers have been made of cast iron or certain alloy compositionswhose efiective period of usefulness or,life under the severe serviceinvolved in automatic glass pressing operations varies from one to sixhours, whereas plungers made in accordance with the present inventionhave been maintained in corresponding service in excess of one hundredand twenty-five hours, including sustained use over twenty-four hourperiods ,without removal for polishing and with no appreciable wear fromthe rubbing action of an associated stripping ring, which action rapidlywears and scores a cast iron plunger, rendering it unfit for use inproducing the necessary quality of commercial pressed glass ware.

Our prior application, Serial No. 667,632, of which this application isa continuation-in-part, describes our improved alloy and a glass machineplunger made therefrom, while the present invention is more particularlydirected to the method of forming and casting articles possessing theimproved alloy composition, which we have found to be particularlysuitable in the manufacture of glass machine plungers as aforesaid.

A preferred specific composition of our improved alloy is carbon 0.90%,molybdenum 1.00%, nickel 3.50%, silicon 1.00%, chromium 12.00%, titanium0.50%, the balance being iron except for incidentals, subject tomanufacture.

A second typical analysis of our improved formula is as follows: Carbon0.82%, chromium 11.65%, nickel 3.43%, molybdenum 1.12%, silicon 1.21%,titanium 0.43%, the balance being iron except for incidental impurities.

While we appreciate the fact that our improved metal chromium alloy canbe made many of the approved furnaces of today, such as crucible, openhearth, converter, direct or indirect arc and all forms of inductionfurnaces, yet we prefer electric melting furnaces due to the fact thatthe alloy requires close temperature control and considerablerefinement. It is essential that the alloy be free from all large slagor nonmetallic inclusions, which, if appearing on the surface, wouldrender the casting unfit for use, During casting, large risers areemployed in order to compensate for the excessive shrinkage encounteredin the casting of this alloy and it has been found to be good practiceto cover the top of the riserwith some form of carbonaceous pipeeliminator.

The structure of the alloy in the cast condition is austenitic, showinga Brinell hardness of about 250, and is machinable. When in thiscondition, the plungers are rough turned to approximate dimensions,allowing only a grind finish on the surfaces exposed to the moltenglass, while the other parts or surfaces are finished to size. The

casting is then subjected to anaccelerated age hardening heat treatment,which is accom= plished by heating to 1750 F. and holding the plungersfrom 1 to 4 hours at this temperature, followed by cooling slowly in thefurnace. This heat treatment increases the Brinell hardness to the orderof 500 to 550, which hardness is essential for long service under thesevere conditions to which these plungers are subjected. The heattreatment also acts as a homogenizing agent which prevents anymeasurable changes in dimensions which may accrue from the repeatedheating and cooling cycles through which the plungers pass in theiroperation. The alloy is -not susceptible to oxidation at glass moldingtemperatures, and therefore, alleviating the necessity, as, in cast ironplungers, of repeated removals for repolishing. The addition of .10% to6.00% titanium has been ,found not only to increase the ease ofmachinability, but also to prevent excessive shrinkage and coolingcracks, but without detrimentally affecting the usefulness of the alloyunder service conditions.

Cast iron plungers in general use today give the resulting glassware afrosty appearance due to the heterogeneity of the material used. Castiron is a mixture ,of metallic crystals, interspersed with softparticles of graphite, and these softer particleswill wear or tear outfirst, leaving the surface in a roughenedcondition and which isimprinted uponthe resulting glassware giving it an undesired appearance.Hand or machine blown glassware is made without the use of plungers andis bright in appearance. This is a much more expensive operation andblown glassware commands a higher price on the market. Bythe use of thealloy made in accordance with the present invention, glassware can bemade by the pressed or pressed blown process, that is, clear, has nofrosty appearance and is comparable with hand blown ware.

Our improved alloy made in accordance with the above mentioned steps, isaustenitic and machinable in the cast condition and martensitic andsubstantially non-machinable in its final heat treated condition. It ishighly resistant to oxidation under temperatures employed in the workingof molten glass. Similarly, it has a high resistance to abrasion, andshows no measurable growth after being subjected to the homogenizingtreatment. While we have described the alloy as particularly suitablefor the manufacture of glass machine plungers, nevertheless we do notlimit ourselves to the use of the alloy in this connection, since it maybe employed in the manufacture of molds, or other machine parts --ducingan alloy casting having substantially the following composition: carbon.80% to 1.0%, chromium 11.50% to 12.00%, nickel 3.40% to 3.75%,molybdenum .90% to 1.25%, silicon .90% to 1.35%, titanium .40% to thebalance being substantially iron, said casting having a Brinell hardnessof the order of 250 and being in austenitic condition as cast, machiningthe said casting to desired shape, then subjecting the casting to anannealing heat cycle in which the casting is maintained at temperaturesof the order of 1700 to 1750 F. for a period of time varying between 1to 4 hours, and then slowly cooling the casting while it is retained inthe furnace zone whereby to increase the Brinell hardness thereof to theorder of 500 to 550 and to homogenize the same against subsequen heatingcycles.

2. The method of producing a cast metallic body for use in themanufacture of pressed articles of glassware, which comprises castingsaid body from a composition composed of substantially the followingingredients in the proportions set forth: carbon 0.80% to 1.0%, chromium11.50% to 12.0%, nickel 3.40% to 3.75%, molybdenum .90% to 1.25%,silicon .90% to 1.35%, titanium .40% to .55%, the balance being ironexcept for incidental impurities, subjecting such a body which is ascast of machinable form in austenitic condition and having a Brinellhardness of 250 to a machining operation to reduce it substantially to adesired form, then subjecting said body to an additional heating cyclein a furnace zone wherein said body is heated to a temperature of theorder of 1700 to 1750 F. for a period of time ranging from 1 to 4 hours,then slowly cooling said body while it is retained in the furnace zone,the final heat treated body possessing a martensitic non-machinablestructure and having a Brinell hardness of 500 to 550 and beinghomogenized against subsequent heating cycles.

7 ALFRED W. GREGG.

RAYMOND H. FRANK.

